The correct answer is to replace the NLB with an ALB and enable sticky sessions using the ALB’s cookie. This works because the ALB’s session affinity mechanism, via the AWSALB cookie, binds a client’s session to a specific EC2 instance, allowing the stateful web application to maintain locally stored session data even as traffic is distributed across multiple Availability Zones. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of how to achieve high availability for stateful apps without rewriting application logic—a common trap is assuming an NLB can handle session stickiness natively, but it lacks the HTTP-layer cookie generation that ALB provides. Remember that ALB sticky sessions are the bridge between stateless load balancing and stateful application requirements. A useful memory tip: “ALB sticks the session, NLB just sends the traffic.”
DOP-C02 Resilient Cloud Solutions Practice Question
This DOP-C02 practice question tests your understanding of resilient cloud solutions. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company runs a stateful web application on EC2 instances behind a Network Load Balancer (NLB) in a single Availability Zone. The application stores session state locally on the instance. The company wants to achieve high availability across multiple AZs with minimal application changes. What should the DevOps engineer do?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Replace the NLB with an ALB and enable sticky sessions (session affinity) using the ALB's cookie.
Option D is correct because replacing the NLB with an ALB and enabling sticky sessions (session affinity) using the ALB's cookie allows the stateful web application to maintain session state across multiple AZs without modifying the application code. The ALB generates a cookie (AWSALB) that binds a client's session to a specific target instance, ensuring subsequent requests from the same client are routed to the same EC2 instance. This achieves high availability across AZs with minimal changes, as the application continues to store session state locally on the instance.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Add more AZs and configure the NLB with cross-zone load balancing.
Why it's wrong here
Without sticky sessions, subsequent requests may go to different instances, breaking session state.
✗
Replace the NLB with an ALB and use ElastiCache for session storage.
Why it's wrong here
This requires application changes to use ElastiCache, which is not minimal.
✗
Use a Multi-AZ RDS instance to store session state.
Why it's wrong here
This requires application changes to use RDS for sessions, which is not minimal.
✓
Replace the NLB with an ALB and enable sticky sessions (session affinity) using the ALB's cookie.
Why this is correct
Sticky sessions ensure that requests from the same client are routed to the same instance, preserving local session state.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume cross-zone load balancing or adding more AZs inherently solves high availability for stateful applications, but they overlook that session affinity is required to keep a client's requests directed to the same instance when session state is stored locally.
Detailed technical explanation
How to think about this question
The ALB's sticky session feature uses a cookie (AWSALB) with a configurable duration (default 1 day) to maintain session affinity. The cookie is set by the ALB on the first request and includes an encrypted hash of the target group and instance ID, ensuring the client is consistently routed to the same instance even across AZs. In a real-world scenario, if the target instance fails, the ALB routes subsequent requests to a new instance, which will not have the session data, so this approach is best combined with session replication or a shared session store for full fault tolerance, but the question specifically asks for minimal application changes.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Resilient Cloud Solutions — This question tests Resilient Cloud Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Replace the NLB with an ALB and enable sticky sessions (session affinity) using the ALB's cookie. — Option D is correct because replacing the NLB with an ALB and enabling sticky sessions (session affinity) using the ALB's cookie allows the stateful web application to maintain session state across multiple AZs without modifying the application code. The ALB generates a cookie (AWSALB) that binds a client's session to a specific target instance, ensuring subsequent requests from the same client are routed to the same EC2 instance. This achieves high availability across AZs with minimal changes, as the application continues to store session state locally on the instance.
What should I do if I get this DOP-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This DOP-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DOP-C02 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.